Pregnancy Due Date Calculator

How Accurate is Your Due Date?

While due dates are helpful for planning, they’re not super precise.

In fact, my wife went over her due date for our first baby by a week, and then was induced before her due date for our second:

• Fewer than 5% of babies are born on their actual due date.
• 80% of babies are born within the two weeks before or after their due date.
• The length of pregnancy can vary based on factors like genetics, maternal health, and whether this is a first pregnancy.

Your due date is more of a guideline to help you and your healthcare provider monitor the pregnancy’s progress and prepare for delivery.

How is Your Due Date Calculated?

There are several methods used to calculate a due date, and medical professionals often rely on more than one:

1. Last Menstrual Period (LMP)

The most common method, Naegele’s Rule, adds 280 days (or 40 weeks) to the first day of your last menstrual period. This assumes a typical 28-day cycle with ovulation occurring around day 14. We adjust this up/down based on your actual cycle.

2. Conception Date

If you know the exact date of conception (e.g., through tracking ovulation or fertility treatments), simply add 266 days to calculate your due date. Easy peasy!

3. Ultrasound Scans

Doctors often adjust the due date based on an early ultrasound, especially if there is a discrepancy between your LMP date and the baby’s development. This is most accurate during the first trimester. Ultrasound scans also led to our babies due dates being changed at some point based on their development.

4. IVF Due Dates

For pregnancies achieved through in vitro fertilization, the due date is calculated based on the date the embryo was transferred. Healthcare providers will provide you with a precise calculation, but we also attempt to calculate it based on the transfer dates in our calculator.

Fascinating Baby Facts About Due Dates

Here are some fun tidbits about birth timing:

• Most common birth month: In the U.S., August tends to have the highest number of births.
• Day of the week: Studies show Tuesday is the most common day for babies to be born.
• Longest pregnancy: The longest recorded human pregnancy lasted 375 days (over 12 months – WOW!!!).
• Seasonal births: Summer months often see higher birth rates (you can thank Thanksgiving, Christmas, and New Years for this).

Why Knowing Your Due Date Matters

Your estimated due date helps guide prenatal care and planning. Here are a few reasons why it’s important:

• Prenatal appointments: Medical providers schedule key tests and checkups based on your pregnancy timeline.
• Baby’s development: The due date helps monitor whether your baby is growing as expected.
• Preparation: It’s easier to plan for maternity leave, pack a hospital bag, and prepare your home when you have an estimated timeline.

Knowing your baby’s due date is an exciting milestone in pregnancy.

While no tool can guarantee the exact date your baby will arrive, a due date calculator gives you a helpful estimate for planning and preparing for your little one’s arrival!